Aluminum alloy for color anodizing



United States Patent 3,475,167 ALUMINUM ALLOY FOR COLOR ANODIZING EarlC. Beatty and Frank L. Howard, Spokane, Wash.,

assignors to Kaiser Aluminum & Chemical Corporation, Oakland, Calif., acorporation of Delaware No Drawing. Continuation-impart of applicationSer. No. 506,396, Nov. 4, 1965. This application May 3, 1967, Ser. No.635,685

Int. Cl. C22c 21/02 U.S. Cl. 75147 3 Claims ABSTRACT OF THE DISCLOSUREAn aluminum alloy suitable for producing extruded shapes and a processfor forming a colored coating on such shapes. The alloy is amodification of 6063 aluminum alloy, including the addition ofmanganese, and the processs is direct current anodizing of the extrudedshape in an aqueous electrolyte containing sulfate ion and aromaticsulfonic acid.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of our co pending application Ser. No. 506,396,filed Nov. 4, 1965, now Patent No. 3,370,943.

BACKGROUND OF THE INVENTION This invention relates to a process forproducing colored anodic oxide coatings on aluminum extrusions, and toan aluminum alloy adapted to receive such coatings.

It is now well known to color-anodize aluminum by processes that produceintegrally colored coatings, as distinguished from colorless coatingsthat are later dyed or pigmented. For example, United States Patents Re.25,566; 3,143,485 and 3,227,639 represent color-anodizing processesemploying aqueous electrolytes containing sulfate ions and certainaromatic sulfonic acids that are substituted with hydroxyl or carboxylgroups or combinations of hydroxyl and carboxyl groups. When aluminum isemployed as the anode in an electric circuit that includes theelectrolyte, integrally colored anodic oxide coatings may be formed incolors ranging from light gold to black. The process may be applied tovirtually any form of aluminum, but it is most often applied to sheetsand extrusions, particularly sheets and extrusions employed forarchitectural purposes. This invention deals with such integrallycolored coatings, and the term coloranodized or terms of similar importrefer to integrally colored coatings.

Although it is easy, on a laboratory scale, to produce colored anodicoxide coatings, many ditficulties arise when producing them forcommerce. Among these difficulties are producing a series ofcolor-anodized articles that match. For example, it is difficultrepeatedly to produce a number of color-anodized extrusions which havethe same color, texture, and glossiness; in other words, the sameappearance so that when used side by side they will match one another.Another problem is to create colors that are usable with one anothereven though the alloys employed are different. Typical of this problemis employing color-anodized sheets as curtain walls in conjunction withcolor-anodized extrusions employed as door frames, spandrels, lintels,column sheaths or similar members.

Metals suitable for extrusion usually have a different composition thanmetals suitable for rolling, and they respond differently to anodizingconditions. Even a series of articles made of the same metal may respondto anodizing differently due to different rnicrostructures. A seriesPatented Oct. 28, 1969 of extrusions may differ due to slightdifferences in the thermal treatment of the extrusion or the billet fromwhich it is formed, and these differences in structure produce differentappearing anodized extrusions even though the billets from which theextrusions were formed had identical composition.

Generally speaking, it is difli'cult to anodize to obtain darker colorson alloys that are constituted to be suitable for extrusion. Forexample, the alloy designated as 6063 alloy by the Aluminum Associationis a widely used extrusion alloy and it is difficult to color-anodizewith darker coatings such as those characterized by colors ranging fromgray to black. The Aluminum Association composition limits for 6063alloy are 0.200.6% silicon, up to 0.35% iron, up to 0.10% copper, up to0.10% manganese, OAS-0.9% magnesium, up to 0.10% zinc, up to 0.10%chromium, up to 0.10% titanium, other elements up to total of 0.15%,balance aluminum. Another difficulty is that the appearance of anodized6063 alloy is extremely sensitive to the thermal treatments to which thealloy is subjected before and during extrusion. In this regard, itshould be pointed out that control of thermal conditions is extremelydifficult. Even such a well known heat treatment as homogenizing cancreate difficulties because ingots are generally homogenized in groupspiled one upon another so that both the heating and the cooling rate ofingots in the interior of the pile is substantially slower than theheating and cooling rates of ingots on the exterior of the pile therebyproducing a different internal structure which in turn produces adifferent response to color-anodizing.

SUMMARY OF THE INVENTION This invention provides an alloy which is amodification of 6063 alloy and which is suitable for extrusion and foraccepting a range of color-anodized coatings, particularly the darkercolored coatings; and provides a process capable of producing coloredcoatings on extruded aluminum. Additionally it provides a process forreducing the effect that variations in thermal treatments have on theresponse an alloy has to an anodizing process. Stated differently, thisinvention provides a means for coloranodizing extruded products in sucha way that the color of the product will depend almost entirely on thecomposition of the metal and the program employed to anodize it therebygiving close control over reproducibility of appearance, and in additionit provides an alloy having substantially the same extrudability as 6063alloy.

DETAILED DESCRIPTION OF THE INVENTION The object of this invention isaccomplished by providing an extrusion alloy which is copper-free andconsists essentially of from about 0.20 to about 0.6% silicon, up to0.35% iron, from about 0.1 to about 0.6% manganese, from about 0.4 toabout 0.8% magnesium, up to about 0.10% of each of chromium, zinc andtitanium, other elements up to a total of 0.15%, balance aluminum. Bythe expression copper-free is meant that copper may be present as animpurity but the amount of copper present should not exceed 0.10%. Apreferred alloy of this invention is one consisting essentially of fromabout 0.3 to about 0.4% silicon, from about 0.15 to about 0.25% iron,from about 0.1 to about 0.2%; manganese, from about 0.45 to about 0.6%magnesium, up to about 0.10% of each of chromium, zinc, and titanium,other elements up to a total of 0.15%, balance aluminum. Allcompositions stated in this specification and the following claims areon a weight percent basis unless stated other- WISE.

The above-specified alloy is homogenized and formed into an extrudedshape. The extruded shape is immersed as the anode in an aqueouselectrolyte which contains in solution from about 0.1% to 4% sulfuricacid or the equivalent amount of sulfate ion and from about 0.09 toabout 0.7 gram mole per liter of an organic sulfonic acid substitutedwith hydroxyl, carboxyl or combinations of hydroxyl and carboxyl groups.Suitable organic acids include 'but are not limited to sulfosalicyclicacid, sulfopl. thalic acid, sulforesorcinol, and lignosulfonic acid.

Anodizing is effected at conditions now well known to thecolor-anodizing art. The temperature of the electrolyte may range fromnear its freezing point to 100 F. or substantially higher, the currentdensity may range from about to 100 amperes per square foot of surfacebeing anodized, the voltage may range from about to 130 volts and thetime is that suflicient to produce the color and thickness of coatingthat is desired; usually less than 120 minutes.

Following are several examples presented to illustrate the presentinvention with typical embodiments of it. The examples are intended tobe illustrative and they have been selected as typical examples todemonstrate the in vention rather than to limit it.

Extrusions were made form several alloys that are useful as extrusionalloys and capable of being color-anodized. Prior to anodizing thealloys were subjected to two tempers that differed substantially fromone another in order to compare the difference in color-anodizingresponse caused by varying thermal treatments of an alloy prior toextrusion. The alloys were also anodized by two different electricalprograms which are both characteristic of those employed tocolor-anodize extrusions.

The temper designated T4 is one of the well known and standard tempersused throughout the aluminum industry with heat treatable aluminumalloys. The T4 temper is obtained by solution heat treating and rapidlycooling the alloy after which it is aged at room temperature to a stablecondition. The temper designated as T6 is also a standard temper wellknown to the aluminum industry for use with a heat treatable alloy. Itis imparted by solution treating an alloy after which it is artificallyaged to approximately maximum tensile properties thereby producing avery strong and stable alloy.

The alloy shown in Table 2 as 6063 alloy is a typical example of the6063 alloy designated in the Aluminum Association classification ofalloys. The specific alloy used contained 0.36% silicon, 0.2% iron,0.005% copper, 0.004% manganese, 0.6% mangnesium, 0.005% chromium, 0.01%zinc, 0.004% titanium, and the remainder substantially aluminumcontaining normal amounts of impurities. The other alloys of theexamples are the same 6063 composition with the specified amounts ofadditional elements. Thus, an alloy designated 6063 plus 0.2% manganeseis the 6063 composition set forth above, but containing 0.2% manganeseinstead of 0.004% manganese.

In Table 1, two anodizing programs are set forth. The first anodizingprogram is employed in all cases in Example 1 and the second anodizingprogram is employed in all cases in Example 2'. Examples 1 and 2 setforth the response to various anodizing treatments to the designatedalloys in both the T4 and the --T6 temper. The color reported for the T4temper is a subjective observation which is accomplished by comparingthe colors obtained with previously established color standards. Thecolors obtained on the specimens with --T6 temper are comparative withrespect to the colors on specimens with -T4 temper. Thus, if the T4temper produces a bronze color and the T6 temper produces a lighterbronze color, the color produced on the T6 temper is reported as lighterwith respect to the color produced on the specimen with a T4 temper.

4 The following Table 1 sets forth the anodizing conditions in each ofExamples 1 and 2:

TABLE 1 Example 1 Example 2 Sulfuric acid (grams/liter) 5 5Sulfosalicylic acid (gram moles/liter). 0. 45 0. 45 Temperature F.) 7575 Initial current density (ampercs/sq i 24 27 Maximum volts 65 60Anodizing time (minutes) 40 45 Total current quantity (amp. hrs/sq. ft.)12.0 10

The results obtained in Examples 1 are set forth in Table 2:

Example 1 above illustrates that the combined eflFect of the alloy ofthis invention and the color-anodizing process produces substantiallydarker color-anodized coatings and coatings that are far less sensitiveto thermal treatments. Although the difference between the colorproduced in the T4 temper and the T6 temper in the manganesecontainingalloys is noticeable, the amount of difference is very slightconsidering that the tempers employed were radically different from oneanother and that they were selected to exaggerate anodizing responsedifferences resulting from thermal history.

The results of anodizing under conditions set forth for Example 2produced anodized alloys as set forth in Table 3 below:

Example 2 also ilustrates that the combination of themanganese-containing extrusion alloy and the color-anodizing process ofthis invention can produce darker colored anodized extrusions, andextrusions which are far less senistive to their thermal history withrespect to coloranodizing response.

Having thus described this invention, what is claimed is:

1. An easily extrudable aluminum base alloy consisting essentially of0.20-0.60% silicon; 0.15-0.25% iron; 0.10- 0.60% manganese; fromGAO-0.80% magnesium; up to 0.10% each of copper, chromium, zinc andtitanium; all other impurities up to a total of 0.15%; and the balancealuminum; and characterized by responding to a coloranodizing program inan electrolyte containing an aromatic sulfonic acid selected from thegroup consisting of sulfosalicylic acid, sulfophthalic acid,sulforesorcinol and lignosulfonic acid and a compound selected from thegroup consisting of metal sulfates and sulfuric acid and combinationsthereof, to produce integrally colored oxide coatings ranging in colorfrom grey to black.

2. An easily extrudable aluminum base alloy consisting essentially ofabout 0.36% silicon; 0.2% iron, 0.4% manganese, 0.6% magnesium and thebalance aluminum with other normal impurities associated therewith.

3. An easily extrudable aluminum base alloy consisting essentially of0.20-0.60% silicon; about 0.35% iron; from 0.10-0.60% manganese; from0.40-0.80% magnesium; up to 0.10% each of copper, chromium, zinc andtitanium; all other impurities up to a total of 0.15% and the balancealuminum; and characterized by responding to a color anodizing programin an electrolyte containing an aromatic sulfonic acid selected from thegroup consisting of sulfosalicylic acid, sulfophthalic acid,sulforesorcinol, and lignosulfonic acid and a compound selected from thegroup consisting of metal sulfates and sulfuric acid and combinationthereof to produce integrally colored anodic oxide coatings ranging incolor from grey to black.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 3/1931 France. 9/1958 Germany.

5 JOHN H. MACK, Primary Examiner Deal t G. L. KAPLAN, Assistant ExaminerKeller et a1.

Fritzlen. U.S. Cl. X.R. Moore et a1 75--147 XR 75-148; 20458 Kampert. 10

